1. Technical Field
This disclosure relates generally to valves for shutting off flow in a pressurized pipe or conduit. More specifically, this disclosure relates to valves that may be installed in a pressurized pipe without shutting off flow to the pipe while the valve is being installed. Still more specifically, this disclosure relates to improvements in the design of a gate valve assembly which increases the pressure rating of the valve and decreases the operating torque required to open and close the valve.
2. Description of the Related Art
Pressurized conduit or pipe systems convey fluids, both liquid and gas, in municipalities, industrial plants, and commercial installations. When originally installed, these conduit systems include certain block valves that may be closed to isolate sections of the pipe for repairs, relocation, or installation of new components into the pipe. When a shutdown is required in a municipal water distribution system, a large area may be deprived of water service. Accordingly, schools, hospitals, commercial and/or industrial facilities may have to be shut down in addition to the inconvenience to residents.
The total length of pipe to be isolated can be greatly shortened by adding additional valves, in conjunction with the preexisting block valves. The additional valves may be of the form that can be installed in a pressurized pipe or conduit without service interruption and with minimal fluid loss. Upon closure of the added valve and completion of the work on the depressurized damaged section of the pipe, the additional valve may be opened or retracted and the block valves are opened, thereby restoring flow through the repaired section of pipe. The additional valves are known in the art under a variety of names, such as a conduit stopper, line stop, conduit line plugger, inserting valve, add-on valve, insertable stopper valve, etc. One example can be found in the commonly assigned U.S. Pat. No. 6,810,903.
Typically, such valves include a chamber or housing disposed adjacent to and communicating with the pressurized conduit. In most cases the chamber is typically rectangular and may be assembled perpendicular and pressure-tight to the outside of the conduit as shown in FIG. 1 of the '903 patent. Communication is established by a process called pressure tapping. This process is well known in prior art, and utilizes a temporary valve, such as a knife valve, to allow the cutting or drilling devices and the new valve to be mounted to the pipe without significant loss of fluid pressure or fluid flow.
After the pipe is cut, the additional valve can then be passed through the temporary valve into the chamber, where it may be held until the pipe needs to be closed. To stop flow, the valve body is then moved from the chamber into the pipe.
Many of the valves added to municipal pipe systems are intended for temporary service, often in emergency situations. However, other additional valves are designed for permanent installation into a pressurized pipe. Each permanent valve is provided with an internal jackscrew-type actuator that allows the valve to be operated as a conventional block valve that is opened and closed by a worker by merely turning a handle or a valve wrench. This type of permanent valve can be used in emergencies in the same manner as a temporary valve and then abandoned.
At least two problems are associated with the currently available valves that may be installed in pressurized pipes. First, the types of valves that utilize a jackscrew actuator may have limited pressure ratings because the pressure applied to the valve body (e.g., a gate or block) is imposed on the jackscrew as rotation of the jackscrew results in the raising or lowering of the valve body. The forces applied to the jackscrew and the valve body are perpendicular to the axis of the jackscrew because the axis of the jackscrew and the axis of the pressurized pipe are perpendicular to each other. Thus, the perpendicular force imposed upon the valve body and jackscrew can cause seal leakage and therefore limit the pressure rating of the valve. A second problem associated with such additional valves added to pressurized pipes is the torque required to open and close the valves. Reducing the operating torque to open and close these types of valves would improve the safety of such operation and reduce the time, effort and costs of carrying out such operations.
Accordingly, improved valves that may be installed in pressurized pipes and conduits are needed.